FR2833936A1 - Porous inorganic material with defined porosity, surface area and pore size, useful as an absorbent, a polymer matrix reinforcing material, an insulating material or a filler for concrete - Google Patents

Abstract

The invention concerns a novel method for preparing high-porosity materials, and in particular high-porosity silicas. The invention also concerns the high-porosity materials obtained by said method, wherein the internal volume of the pores represent in general at least 80 % of the material total volume, which have a general specific BET surface area not less than 800 m<sp>2</sp>/cm<sp>3</sp> of the material, and which have pores of dimensions ranging between 2 and 20 nm, associated with pores of dimensions ranging between 50 and 250 nm. The invention also concerns the use of said materials, in particular as reinforcing materials, absorbent materials or insulating materials.

Description

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The present invention relates to an original process for preparing high porosity mineral materials, useful in particular as absorbent materials, reinforcing materials in low density materials, or sound or thermal insulating materials. The invention also relates to porous mineral materials of specific structure obtained according to this process, and in particular to silicas of high porosity which can be produced according to the process of the invention.

Generally ; a porous mineral material useful as an absorption material, a reinforcing material in a material of low density, or an insulating material has a high porosity, that is to say that the internal volume of its pores generally represents a large fraction of the total volume of the material, typically at least 60% of the total volume of the material, and advantageously at least 75%. A material suitable for this type of use also advantageously has a high specific surface area, advantageously at least equal to at least equal to at least 600 m2 per cm3 of material, and preferably at least equal to 800 m2 per cm3 of material.

Numerous methods of preparing porous inorganic materials capable of exhibiting such characteristics are currently known. In this regard, mention may in particular be made of the processes for the preparation of high pore volume silicas described for example in the Journal of Colloid and Interface Science, volume 197, pp. 353-359 (1998).

The inventors have now discovered that it is possible to synthesize mineral materials of very high pore volume and of high specific surface, by carrying out the synthesis of a mineral matrix from an inorganic precursor, in a medium comprising , in specific amounts and proportions, organic polymers of dendritic nature and nonionic surfactants.

The inventors have further demonstrated that, in the materials synthesized, a large fraction of the pore volume corresponds to

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pores of small internal dimensions, typically less than 40 nm. The inventors have discovered that this characteristic is in particular capable of giving the materials good absorption qualities in certain applications, and especially that, when these materials are incorporated as reinforcing material in polymer matrices, the presence, in quantity large, small pores, difficult to access by polymers, allows polymer materials having both high mechanical strength and low densities.

On the basis of these findings, one of the aims of the present invention is to provide a new process for preparing high porosity materials suitable in particular for use as absorbent materials, reinforcing materials in low density materials, or more sound or thermal insulating materials.

The object of the invention is also to provide new inorganic materials exhibiting very high porosity, that is to say which notably exhibit a high pore volume, associated with a high specific surface area. The aim of the invention is thus in particular to provide silicas of very high porosity, having a structure which is particularly suitable for performing the role of an absorption matrix, or for enabling the reinforcement of polymer matrices of low density.

Thus, according to a first aspect, the present invention relates to a process for preparing a mineral material of high porosity comprising the successive steps consisting in: (a) producing a homogeneous aqueous or hydro-alcoholic medium comprising: (i) a mineral precursor of a mineral phase P; (ii) dendritic organic polymers comprising surface functionalities (F) capable of forming strong bonds with the mineral precursor (i) or with the mineral phase P; and (iii) nonionic surfactants,

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said medium being such that, if we denote by n (,) the total amount of mineral precursor (i), by n (i,) the total amount of polymers (ii), by n (F) the total amount of functionalities of surface (F) carried by the polymers (ii) and capable of forming strong bonds with the mineral precursor (i) or with the mineral phase P, and by n (ill) the total quantity of nonionic surfactants (iii) : - the molar ratio n (ij! n (F) is between 2 and 50; - the molar ratio n (l) ln (ll) is between 100 and 5000; and - the molar ratio n / n) is included between 0.05 and 0.30; (b) within the medium thus obtained, forming a solid mineral phase from the mineral precursor, the total amount of solvent (s) introduced during steps (a) and (b) being such that the concentration of said polymers (ii) in the medium obtained at the end of step (b) is between 0.01 and 10 millimoles per liter, whereby an inorganic material of porous structure integrating dendritic organic polymers is produced, and optionally, nonionic surfactants within its pores; and (c) removing dendritic organic polymers and nonionic surfactants within the resulting structure, whereby a porous inorganic material of high porosity is obtained.

One of the essential compounds to be used in the process of the invention is the mineral precursor (i). In general, the term “mineral precursor” is understood to denote, within the meaning of the invention, a compound which is soluble or dispersible in an aqueous or hydro-alcoholic composition under certain conditions, in particular under certain pH conditions (conditions known as "stability"), this compound being capable of leading to the formation of a mineral phase P under other conditions, for example under other pH conditions or in the presence of certain particular chemical compounds (so-called "condensation conditions "). During step (a) of the process of the invention, the mineral precursor is generally introduced in the form of a solution or a dispersion under its conditions of stability, and the medium is then modified, in step (b), so as to place oneself in the conditions of

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condensation. In the context of the process, in order to control the kinetics of formation of the mineral phase, it may be advantageous to use catalysts or even depot bases, such as urea for example.

According to a particularly advantageous embodiment of the process of the invention, the mineral precursor (i) used is a metallic compound, generally soluble in water, ethanol and / or water / ethanol mixtures, this metallic compound. being based on a metal M, advantageously chosen from silicon, aluminum, zirconium, or even rare earths, the term “rare earth” designating, within the meaning of the present invention, a chosen metal element among the yttrium and the lanthanides (the lanthanides are the metallic elements whose atomic number is included, in an inclusive way, between 57 (lanthanum) and 71 (lutetium)). Preferably, the metal M denotes silicon. According to this particular embodiment, the total quantity n (i) of mineral precursor (i) to which reference is made for the molar ratios n (F / n (,) and n (n (,) which characterize the medium of the step (a) is equal to the quantity of metal M introduced. In this context, the quantity of precursor in the middle of step (a) is most often such that the concentration of metal M in the middle of step (a) is between 0.1 and 100 millimole per liter, and preferably at least equal to 1 millimole per liter.

According to a particularly advantageous embodiment of the invention, the inorganic precursor (i) of step (a) can comprise (or even consist essentially of) a silicon alkoxide such as sodium tetraethyl-orthosilicate TEOS or even a halide silicon such as silicon tetrachloride SiCl4. In this case, the precursor is generally introduced into step (a) in the form of an aqueous or hydro-alcoholic solution with a pH of between 8 and 11, and step (b) generally consists in bringing the medium at a pH between 4 and 7.5, and in adding to the medium obtained a condensation catalyst, generally a nucleophilic agent, whereby the mineral phase formed at the end of step (b) comprises (or is essentially consisting of) silica Si02. The condensation catalyst used in this context is generally a metal fluoride, most often NaF, advantageously in aqueous solution, used in an amount such as the molar ratio

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fluoride / silicon is advantageously between 0.01 and 0.05, and preferably at most equal to 0.03
According to another advantageous embodiment, the inorganic precursor (i) can comprise (or even consist essentially of) a metal silicate, in particular an alkali silicate such as sodium silicate.

In this case, it is introduced, most often, in the form of an aqueous or hydro-alcoholic solution with a pH of between 10.5 and 13.5, and step (b) generally consists in bringing the medium to step (a) at a pH of between 8.5 and 10, and preferably between 8.5 and 9.5, whereby the mineral phase formed comprises (or essentially consists of) silica SiO 2.

According to another particular embodiment that can be envisaged, the inorganic precursor (i) can also comprise an aluminum alkoxide, or else an aluminum salt, such as aluminum nitrate. The mineral precursor (i) is then generally introduced in the form of an aqueous solution with a pH of less than 2, and, in step (b), the medium is generally brought to a pH greater than 2, and preferably between 3 and 6, whereby an inorganic phase based on aluminum oxy-hydroxide AIOOH is formed.

According to yet another possibility, the inorganic precursor used can comprise a zirconium salt, such as a nitrate or a zirconium chloride. The mineral precursor (i) is then generally introduced in the form of an aqueous solution with a pH of less than 0.5, and, in step (b), the medium is generally brought to a pH greater than 0.5, preferably between 1 and 4, whereby a mineral phase based on zirconia ZrO2 is formed.

The mineral precursor used can also comprise a rare earth salt, such as a chloride or a nitrate (advantageously a lanthanum chloride or nitrate). As a general rule, the mineral precursor (i) is then introduced in the form of an aqueous solution with a pH of less than 4, and, in step (b), the medium is generally brought to a pH of between 4 and 9 , and preferably between 4.5 and 8.5, whereby a mineral phase based on lanthanum hydroxide La (OH) s is formed.

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A second essential constituent to be used in the process of the invention is the dendritic organic polymer (ii). For the purposes of the present description, the term “dendritic organic polymer” denotes, broadly, a polymer having a branched structure capable of being obtained by polymerization (or copolymerization) of organic monomer units with a functionality greater than 2. chemical functions present at the ends of the branches of such a structure are designated by the term "surface functionalities". By definition, the number of surface functionalities on a dendritic polymer is greater than 2.

-. 1des liaisons fortes avec le précurseur minéral (i) ou avec la matrice minérale P, et avantageusement au moins 10 fonctionnalités de surface (F) de ce type, de préférence au moins 20, et encore plus préférentiellement au moins 40. On préfère généralement que le nombre de fonctionnalités de surface (F) de ce type soit tel que la densité de présence de fonctionnalités de type (F) à la surface des polymères dendritiques (ii) mis en oeuvre soit comprise entre 0,1 et 10 fonctionnalités (F) par nm2. Avantageusement les polymères (ii) présente sur leur surface au moins 1 fonctionnalité (F) par nm2, de préférence au moins 2 fonctionnalités (F) par nm2. Characteristically, in the dendritic polymers (ii) used in the process of the present invention, at least one of the surface functionalities is a functionality (F) capable of forming strong bonds with the inorganic precursor (i) or with the mineral matrix P and, preferably, the dendritic polymers (ii) used according to the invention each comprise at least two functionalities (F) capable of forming

-. 1 strong bonds with the inorganic precursor (i) or with the mineral matrix P, and advantageously at least 10 surface functionalities (F) of this type, preferably at least 20, and even more preferably at least 40. It is generally preferred that the number of surface functionalities (F) of this type is such that the density of presence of functionalities of type (F) at the surface of the dendritic polymers (ii) used is between 0.1 and 10 functionalities (F) by nm2. Advantageously, the polymers (ii) present on their surface at least 1 functionality (F) per nm2, preferably at least 2 functionalities (F) per nm2.

The "strong bonds" induced by the intermediary of the surface functionalities (F) present on the dendritic polymers (ii) between the mineral precursor (i) or the mineral matrix P and said dendritic polymers (ii) are generally complexing bonds or electrostatic.

Thus, when the inorganic precursor (i) used is a compound exhibiting a charge under the conditions of implementation of the process (for example

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example a silicon alkoxide, such as TEOS sodium tetraethyl-orthosilicate at a pH between 4 and 9, an alkali silicate such as sodium silicate at a pH between 5 and 9.5 or else a metal cation such as 'an aluminum, zirconium or rare earth cation) the surface functionalities (F) are generally chosen from functions of opposite charge, that is to say from cationic functions such as amine groups in their protonated forms, when the precursor (i) has a negative charge, or from anionic functions, in particular carboxylate, phosphate, phosphonate or sulfate functions, when the precursor (i) has a positive charge.

The surface functionalities (F) can also be nonionic chemical functions, insofar as these functions are capable of developing sufficiently strong bonds with the precursor (i). Thus, in the particular case where the inorganic precursor (i) is a silicon alkoxide, such as sodium tetraethyl-orthosilicate TEOS, the surface functionalities (F) can be alkoxysilane functions, and in particular Si-functions (OR ) 3, where R denotes a C1-C8 alkyl group.

Advantageously, in this specific context, it may be - Si (OEt) 3 functions.

Furthermore, it is preferred that the branched structure of the dendritic organic polymers (ii) used within the meaning of the invention have a substantially globular shape. Whether or not the polymers (ii) have such a globular shape, it is preferred that, in the mediums of steps (a) and (b), the average dimensions of the branched structure developed by these polymers are between 1 and 20 nm. Advantageously, these dimensions are less than or equal to 10 nm, and preferably less than or equal to 5 nm.

The dendritic organic polymers (ii) used according to the invention can be dendrimers. By “dendrimer” is meant a dendritic polymer exhibiting a tree polymer structure characterized by a regular arrangement of its tree structure, with

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génération". Un dendrimère dit"de n'e génération"est obtenu au bout de n étapes de greffage de ce type (n étant un entier allant généralement de 1 à 10). Pour plus de détails en ce qui concerne les molécules de type dendrimères, on pourra notamment se reporter aux exemple de structures de ce type décrites dans l'article de Tomalia et al. dans Angewandte Chemie, Int. advantageously the existence of symmetry within said structure. Such a polymer structure, sometimes designated by the term of "fractal" structure, is generally obtained by a first step of condensation of monomers having more than two functions reactive in polymerization on a molecule called "core molecule" having at least two functions capable of react with one of the reactive functions carried by the monomers. At the end of this step, a so-called “first generation dendrimer” polymer molecule is obtained, carrying surface functionalities which are reactive in polymerization, onto which it is possible to again graft by condensation monomers having at least two functions reactive in polymerization, whereby we obtain a dendrimer called "second

generation ". A so-called" nth generation "dendrimer is obtained after n grafting steps of this type (n being an integer generally ranging from 1 to 10). dendrimers, reference may in particular be made to the examples of structures of this type described in the article by Tomalia et al in Angewandte Chemie, Int.

Ed. Engl., Vol. 29, pp. 138-175 (1990).

The dendritic organic polymers of the invention can also be so-called “hyperbranched” polymers. For the purposes of the description, the term “hyperbranched polymer” will be understood to mean a dendritic polymer having a structure capable of being obtained by random polymerization (or copolymerization) of monomer molecules having a functionality greater than 2 (typically equal to 3), optionally as a mixture. with monomer molecules exhibiting a functionality equal to 2. By way of example of such hyperbranched polymers, mention may for example be made of the polyphenylenes described by YH Kim and OW Webster in Macromolecules, vol. 25, pp. 5561-5572 (1192), the polyamides or polyesters with a dendritic structure described in applications WO 92/08749 or WO 97/26294 or else the polymers described in applications WO 93/09162, WO 95/06080 or WO 95 / 06081.

Whatever their exact nature, it is generally preferred that the polymers (ii) be present at a concentration at least equal to 0.01 millimoles per liter in the medium of step (a). Characteristically, the

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concentration of polymers (ii) in the medium of step (a) is chosen so that, in the medium obtained at the end of step (b), the concentration of said polymers (ii) is between 0.01 and 10 millimoles per liter, preferably between 0.05 and 1 millimoles per liter, and even more advantageously between 0.1 and 0.5 millimoles per liter. In this context, the polymer concentration (ii) in the medium of step (a) is in particular to be adapted as a function of the treatment of the precursor (i) envisaged in step (b), which often passes through the addition of aqueous or hydro-alcoholic solutions of acids, bases or condensation "catalysts", which induces a dilution of the synthesis medium. In general, the aforementioned concentrations are also also chosen so that the ratio Vp / (Vp + V (,,)) (where Vp represents the volume of the mineral phase P formed from the precursor (i), and V (li) denotes the total volume occupied by the polymers (ii) in solution) is between 0.1 and 0.5, and preferably between 0.2 and 0.4.

Another essential compound to be used in the process of the invention is the surfactant (iii). As regards this surfactant, the work of the inventors has shown that, in order to obtain a significant porosity for the material obtained at the end of the process of the invention, it is necessary that the interactions between this surfactant (iii ) and the precursor (i) or the mineral phase P formed from this precursor are weaker than the interactions existing between the functionalities (F) of the polymers (ii) and the precursor (i) or the mineral phase P formed from of this precursor.

In this context, the surfactant (iii) is characteristically a nonionic surfactant.

The nonionic surfactant (iii) is advantageously a block copolymer having at least one poly (ethylene oxide) block.

Thus, and this very particularly when the inorganic precursor (i) is a compound based on silicon, of the silicon alkoxide or alkali silicate type, the surfactants (iii) can for example be poly (ethylene oxide) triblock copolymers - poly (propylene oxide) -poly (ethylene oxide) called
PEO-PPO-PEO, or even block copolymers comprising a poly (ethylene oxide) block comprising from 2 to 10 ethoxyl groups, of

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preferably between 4 and 8 ethoxyl groups, associated with an alkyl or alkanol chain comprising from 8 to 18 carbon atoms, preferably between 10 and 14 carbon atoms, such as the surfactants sold under the brand names Brij 30, Brij 35, Brij 52, Brij 56, Brij 58, Brij 72, Brij 76, or Brij 78, by the company Fluka, or also the surfactants marketed by Sigma under the brand name of Tergitol. Particularly advantageous nonionic surfactants (iii) are block copolymers comprising a poly (ethylene oxide) block comprising between 4 and 8 ethoxyl groups, associated with an alkyl chain comprising 12 carbon atoms.

One of the important parameters to be controlled in the process of the invention is the ratio of the various compounds (i), (ii) and (iii) used. In this regard, the inventors have demonstrated that it is possible to produce very high porosity materials by adjusting the molar ratios n (lyn (F) and n (i) / n (j ,,), where n ( F), n (i) and n,) are as described above.

Without wishing to be bound in any way to a particular theory, it seems to be able to be argued that, subject to carrying out the process of the invention so as to obtain, at the end of step (b), a concentration of polymers ( ii) in the medium between 0.01 and 10 millimoles per liter, and with molar ratios n (, / n (F), n (I) / n (II) and n (I) / n (III) in the ranges indicated above during step (b) of the process of the invention, the precipitation of a mineral phase around the polymers (ii), these polymers being found dispersed in a very dilute manner within the synthesis medium, this whereby we ultimately obtain a highly porous mineral structure.In this context, the adjustment of the molar ratio n (, / n (F) seems to make it possible to optimize the interactions between the compounds (i) and (ii), and the ratio n (iyn (ili) seems to influence the dispersion of polymers within the medium.

The inventors have demonstrated that, in the most general case, it is advantageous for the ratio n (, / n (F) to be at least equal to 5, and preferably at least equal to 7. It is moreover the ratio. more often preferable for this ratio n (lys (F) to be less than or equal to 20, and advantageously less than or equal to 15. Thus, this ratio can advantageously be between 8 and 12 in the

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general case. These values are in particular adapted in the specific context of the use of a precursor (i) based on silicon, of the silicate or silicon alkoxide type, this ratio n (,) / n (F) then being even more preferably between 9 and 11, preferably between 9.5 and 10.5.

It has also been demonstrated by the inventors that the ratio n (,, they (,) is preferably at least equal to 0.07, and advantageously at least equal to 0.09. This ratio n / n (, ) is also advantageously less than 0.2, and preferably less than 0.17. Thus, this ratio can typically be between 0.1 and 0.15. In particular in the specific context of the implementation of a precursor (i) based on silicon, such as a silicate or a silicon alkoxide, this ratio n (,,,) / n (,) is preferably between 0.11 and 0.14.

As a general rule, the formation of the mineral phase of step (b) can be carried out at a temperature of between 10 and 100 C. It is preferably carried out between 20 and 80 C, when the precursor (i) is an alkoxide. silicon or a silicate, in particular a sodium silicate. In the context of the use of a depot base, in particular of urea type (for example with a precursor (i) of aluminum or rare earth salt type), the formation of the mineral phase of step (b ) is advantageously carried out between 60 and 100oC.

Furthermore, step (b) is preferably carried out by placing itself under the conditions of a homogeneous growth regime for the mineral phase being formed. In this context, step (c) can in particular advantageously comprise an ultrasonification step, carried out if necessary so as to achieve homogenization of the reaction medium.

Preferably, step (b) comprises a maturing step, generally carried out by leaving the medium to stand at a temperature ranging from 20 to 100 ° C., and for a variable period of time, most often between
1 and 24 hours.

Step (c) of the process of the invention, which consists in removing the polymers (ii) and the surfactant (iii) present in the porous mineral structure

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typiquement avec un gradient de montée en température compris entre 0, 5 C par minute et 50C par minute, et avantageusement à raison d'une augmentation d'au plus 2, 5 C par minute. Le traitement thermique peut avantageusement comprendre au moins un pallier intermédiaire de maintien à une température comprise entre 150 et 300 C, généralement pendant une durée de une à deux heures, puis un deuxième pallier, le plus souvent à une température au moins égale à 400 C, de préférence au moins égale à 5000C (typiquement à une valeur sensiblement égale à 5500C). obtained at the end of step (b) can be carried out by any means known per se. Most often, the medium obtained at the end of step (b) and the possible ripening is filtered and washed on a filter, then the polymers (ii) and the surfactants (iii) can be removed by washing or entrainment with organic solvents followed by drying and / or heat treatment. The polymers (ii) and the surfactants (iii) can more simply be directly removed by heat treatment of the material obtained at the end of the drying, if necessary at a temperature generally at least equal to 250 ° C. to allow calcination of the organic compounds. (ii) and (iii), but at a temperature preferably at most equal to 600 ° C., in particular so as not to affect the specific surface, the stability and / or the porosity of the material. This heat treatment is preferably carried out with a slow rise in temperature,

typically with a temperature rise gradient of between 0.5 ° C. per minute and 50 ° C. per minute, and advantageously at a rate of an increase of at most 2.5 ° C. per minute. The heat treatment can advantageously comprise at least one intermediate stage for maintaining a temperature of between 150 and 300 ° C., generally for a period of one to two hours, then a second stage, most often at a temperature at least equal to 400 ° C. , preferably at least equal to 5000C (typically to a value substantially equal to 5500C).

According to a second aspect, the present invention also relates to the original materials of high porosity which can be synthesized according to the process of the invention.

In general, a material obtained according to the process of the present invention is a porous mineral material within which the total internal volume of the pores represents at least 80%, most often at least 85%, and advantageously at least 90% of the total volume. of the material. This internal volume of the pores within a material according to the invention can in particular be determined by methods for measuring nitrogen adsorption and desorption isotherms, associated with mercury porosimetry measurements known to those skilled in the art. job.

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Most often, within a material obtained according to the process of the invention, the total internal volume of the pores of dimensions less than or equal to 40 nm represents at least 60% of the total volume of the material, generally at least 70% of the material. total volume of the material, and preferably at least 80% of the total volume of the material. The total internal volume of the pores of size less than or equal to 40 nm to which reference is made here can in particular be determined by measurements of adsorption and desorption of nitrogen on a sample of the material.

In addition, the porous materials of the invention generally have a BET specific surface area greater than or equal to 800 m2 per cm3 of material, this BET specific surface area being most often at least equal to 1000 m2 per cm3 of material, advantageously at least equal to 1200 m2 per cm3 of material, and even more preferably at least equal to 1400 m2 per cm3 of material. In most cases, the BET specific surface area of the materials of the invention is between 1000 and 2000 m2 per cm3 of material. The BET specific surface to which reference is made here is the specific surface area of the material as measured according to the so-called "BRUNAUER-EMMET-TELLER" method described in the Journal of the American Chemical Society, vol. 60, page 309 (February 1938).

In addition, the materials of the invention typically comprise: (1) pores with dimensions between 2 and 20 nanometers, these pores generally having dimensions not less than 3 nm, and most often not less than 4 nm ; and (2) pores with dimensions between 50 and 250 nanometers, these pores generally having dimensions not greater than 200 nanometers.

The presence of the pores (1) and (2) characteristic of the materials of the invention can in particular be demonstrated by observation by transmission microscopy of an ultramicrotomic section of said material. Most often, this type of observation makes it possible to highlight, in addition to

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pores (1) and (2), a whole range of pores of intermediate dimensions.

Thus, it is not uncommon to observe, in a material according to the invention, a relatively continuous range of pores between 2 and 250 nm, and in general between 3 and 200 nm. Such a continuous range of pores of variable dimensions can also be demonstrated by nitrogen absorption / desorption measurements of the type mentioned to determine the pore volume of the material.

Without wishing to be bound in any way to any theory, it seems to be able to be argued that the presence of the pores (1) comes at least in part from the fact that, under the specific conditions of the process of the invention, the mineral material is formed. around dendritic polymers (ii), or aggregates of a few dendritic polymers (ii), with which the precursor (i) develops strong interactions, which results in the material formed at the end of step (b), zones of the mineral material which encapsulate dendritic polymers or aggregates of dendritic polymers, of dimensions generally between 2 and 20 nm. It seems that it can be argued that it is these zones trapping dendritic polymers which are at least in part at the origin of the pores (1) observed at the end of step (c). In other words, one can schematically consider at least part of the pores (1) as "hollow shells" which initially contained dendritic polymers (ii). To express it still differently, it seems that at least part of the pores (1) can be considered as resulting from what is commonly called a “texturing” of the mineral matrix, by the polymers (ii).

The pores (2), also characteristic of the materials of the invention, for their part reflect the original process of formation of the mineral matrix under the conditions of implementation of the process of the invention. In this regard, it seems in fact to be able to be argued that, in particular due to the weak interaction between the surfactants (iii) used and the mineral precursor, the formation of the mineral phase around the dendrimers (ii) which is mentioned below. above, in the context of the formation of the pores (1) takes place in a manner that is both unorganized and diluted within the reaction medium, this

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which seems to be at the origin of the appearance of pores (2) of relatively large dimensions.

In fact, it can be considered, schematically, that the material of the invention is constituted by a joining of porous objects whose internal pores constitute at least in part the pores (1). Under the specific conditions of the process of the invention, this “stack of porous objects” is produced with a very low volume occupation by the solid phase, whereby a relatively large space is obtained between the shells, this pore space comprising, among others, the pores (2).

In fact, most often, when an ultramicrotomic section of a material according to the invention is observed by transmission electron microscopy, it is observed that the structure presented by the material can be described as a joining of hollow objects, generally substantially spherical, with external dimensions most often between 4 and 28 nanometers, advantageously less than or equal to 20 nm, preferably less than or equal to 15 nm, and even more preferably less than or equal to 10 nm, and having a wall thickness of between 1 and 8 nm, and preferably between 2 and 5, the internal diameter of these hollow objects generally being between 2 and 20 nm, preferably less than or equal to 15 nm, advantageously less than or equal to 10 nm, and again more preferably less than or equal to 8 nm. These hollow objects, joined together, then themselves define a porous structure which generally has pores of dimensions between 10 and 250 nm. Thus, in certain particular cases, it is observed that a material according to the invention can be in the form of a structure similar to that of a percolation cluster of hollow objects that are substantially spherical and of dimensions between 4 and 28. nm.

Whatever their exact structure, it is preferred that the porous inorganic materials of the invention are materials comprising at least one metal oxide, hydroxide or oxy-hydroxide of a metal M preferably chosen from silicon, aluminum. , zirconium or earths

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rare. This oxide, hydroxide or oxy-hydroxide is preferably a silica, an aluminum oxy-hydroxide, an aluminum hydroxide, a zirconium oxide, a rare earth hydroxide, or a rare earth oxide. Where appropriate, the oxides, hydroxides and / or oxy-hydroxides present are preferably major constituents of the mineral material, ie they preferably represent at least 50% by mass, preferably at least 80%, and advantageously at least 90% by mass in said material.

Advantageously, the mineral material of the invention consists essentially of one or more metal oxide (s), hydroxide (s) and / or oxy-hydroxide (s), preferably of the aforementioned type.

According to a particularly advantageous embodiment, the material of the invention consists essentially of silica.

In the specific case where the material of the invention consists essentially of silica, it is preferred that the pore volume of said material, namely the internal volume of all of its pores, is at least equal to 2 cm3 per gram of material, and advantageously at least 2.5 cm3 per gram of material, the internal volume of its pores of dimensions less than or equal to 40 nm preferably being at least equal to 1.5 cm3 per gram of material, and advantageously at least at less 2 cm3 per gram of material. Generally, the pores present in a material according to the invention essentially consisting of silica comprise (1) pores with dimensions between 5 and 20 nm and (2) pores with dimensions between 50 and 200 nm.

Still in the case of a material consisting essentially of silica, it is also preferred that the material has a BET specific surface, as measured according to the so-called "BRUNAUER-EMMET-TELLER" method described in the Joumal of the American Chemical Society, vol . 60, page 309 (February 1938), at least equal to 400 m2 per gram, this BET specific surface area generally being at least equal to 500 m2 per gram, most often at least equal to 600 m2 per gram, and advantageously at least equal to at 700 m2 per gram. In most cases, the specific surface

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BET materials of the invention can reach values greater than or equal to 800 m2 per gram, or even at least equal to 900 m2 per gram.

Typically, a high porosity silica according to the invention has a BET specific surface area of between 400 and 1000 m2 per gram.

In particular taking into account their very high porosity, in particular in the field of pores of dimensions less than or equal to 40 nm, and of their high specific surface, the materials of the invention can advantageously be used as absorbent materials, materials. of reinforcement for polymer matrices, in particular of elastomer or polyamide type (where they make it possible to obtain reinforced polymer matrices of low density and having good mechanical strength properties), or else as insulating materials; in particular as thermal and / or sound insulators. The materials of the invention can also prove to be useful as filler for concrete compositions. These particular uses constitute another particular object of the present invention.

The various objects and advantages of the present invention will emerge even more clearly in view of the various illustrative examples of the preparation of high porosity silicas which are set out below, as well as in view of the appended figure which is a photograph taken under microscopy. transmission electron on an ultramicrotomic section of a material produced according to the method of the invention.

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Example 1
In a polyethylene flask, 0.23 g of Tergitol 15-S-12 (sold by the company Sigma) was dissolved, with stirring, in 10 g of distilled water at 50 C.

To the solution obtained, was added, still with stirring, 0.17 g of a so-called G4NEt2 dendrimer, placed in 5.8 g of distilled water. Stirring was allowed to continue at 50 ° C. until the medium was completely homogenized.

dans laquelle A représente un groupement trivalent 0-Ph-CH=N-N (-CHs)-P (=S), où Ph représente un noyau phényl divalent substitué en position para. The G4NEt2 dendrimer used is a 4th generation dendrimer which has the following formula:

in which A represents a trivalent group 0-Ph-CH = NN (-CHs) -P (= S), where Ph represents a divalent phenyl ring substituted in the para position.

A method of preparing the G4NEt2 dendrimer is in particular described in The Journal of the American Society, 117, 20, pp. 5470-5476 (1995).

To the medium obtained following the addition of the dendrimer and the homogenization, was added, with vigorous stirring, 1 g of absolute ethanol, then, dropwise, 0.52 g of TEOS (Tetra Ethyl Ortho Silicate Si (OEt ) 4 sold by the company Aldrich; purity 98%). The medium then became slightly cloudy.

A 0.25 N HCl solution was then added to the medium obtained until a pH of 5.5 was obtained. The medium was then subjected to ultrasonication for 10 minutes, whereby a milky solution was obtained.

The mixture was then allowed to stand for 12 hours, and a clear medium was obtained. 0.27 g of a solution of

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1 wt% NaF in distilled water, whereby the formation of a precipitate was observed after 10 minutes.

The medium was then placed (still in the polyethylene flask) in an oven at 60 ° C. for 48 hours.

The solid obtained at the end of these steps was washed on a filter with 500 ml of distilled water, then it was dried for 12 hours in an oven at 60 C.

The temperature of the solid was then gradually raised from 60 ° C. to 200 ° C., at a gradient of 2 ° C. per minute, then the solid was left at 200 ° C. for one hour. The temperature of the solid was then gradually increased from 200 ° C. to 550 ° C., still at a rate of a gradient of 2 ° C. per minute, then the solid was left at 550 ° C. for 5 hours. The oven was then allowed to cool to a temperature below 50 ° C. before removing the calcined solid.

d'absorption/desorption d'azote sur un échantillon du matériau a été mesuré égal à 2 cm3fg. The BET surface measured for the solid obtained is equal to 945 m / g, and the pore volume determined from the plot of an isotherm

absorption / desorption of nitrogen on a sample of the material was measured equal to 2 cm3fg.

On transmission microscopy photographs of ultramicrotomic sections of the solid obtained, a particular structure was observed which can be described as a joining of small spherical porous objects whose internal dimensions are between 5 and 20 nm, these contiguous objects forming them- even a porous structure having pores of variable dimensions, ranging from 25 to 200 nm. The attached Figure is one of the most characteristic pictures obtained in this context.

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Example 2
In a polyethylene flask, 0.46 g of Tergitol 15-S-12 (sold by the company Sigma) was dissolved, with stirring, in 31.5 g of distilled water previously brought to 50 C.

To the solution obtained was added, still with stirring, a solution prepared by adding 0.06 g of a so-called G4NSi (OEt) 3 dendrimer, to a mixture of 2 g of ethanol and 1 g of anhydrous THF tetrahydrofuran . raised to 50 C.

The medium was left under stirring at 50 ° C. until homogenization.

dans laquelle A représente un groupement trivalent 0-Ph-GH=N-N (-CH3)-P (=S), où Ph représente un noyau phenyl divalent substitué en position para. The G4NSi (OEt) 3 dendrimer used is a 4th generation dendrimer which has the following formula:

in which A represents a trivalent group 0-Ph-GH = NN (-CH3) -P (= S), where Ph represents a divalent phenyl ring substituted in the para position.

The medium obtained was kept under stirring following the addition of the dendrimer and the homogenization, and 1.04 g of TEOS (Tetra Ethyl Ortho Silicate Si (OEt) 4 sold by the company was introduced dropwise. Aldrich company; 98% purity). The medium then became slightly cloudy.

A 1N HCl solution was then added to the medium obtained until a pH of 5.5 was obtained. The medium was then subjected to ultrasonication for 10 minutes, whereby a milky solution was obtained.

The mixture was then allowed to stand for 12 hours, and a clear medium was obtained. 0.52 g of a 1% by mass NaF solution in distilled water was then added, whereby the formation of a precipitate was observed after 10 minutes.

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The medium was then placed (still in the polyethylene flask) in an oven at 60 ° C. for 48 hours.

The solid obtained at the end of these steps was washed on a filter with 500 ml of distilled water, then it was dried for 12 hours in an oven at 60 C.

The temperature of the solid was then gradually raised from 60 ° C. to 200 ° C., at a gradient of 2 ° C. per minute, then the solid was left at 200 ° C. for one hour. The temperature of the solid was then gradually increased from 200 ° C. to 550 ° C., still at a rate of a gradient of 2 ° C. per minute, then the solid was left at 550 ° C. for 5 hours. The oven was then allowed to cool to a temperature below 50 ° C. before removing the calcined solid.

The BET surface measured for the solid obtained is equal to 500 m / g, and the pore volume determined from the plot of an absorption / desorption isotherm of nitrogen on a sample of the material was measured equal to 1.5 cm3fg.

On transmission microscopy photographs of ultramicrotomic sections of the solid obtained, a particular structure was observed which can be described as a joining of small spherical porous objects whose internal dimensions are between 5 and 20 nm, these contiguous objects forming them- even a porous structure having pores of variable dimensions, ranging from 25 to 200 nm.

Claims (25)

1. Porous mineral material within which the total internal volume of the pores represents at least 80% of the total volume of the material, said material also having a BET specific surface area greater than or equal to 800 m2 per cm3, and said material comprising (1) pores with dimensions between 2 and 20 nanometers and (2) pores with dimensions between 50 and 250 nanometers. 2. Porous mineral material according to claim 1, within which the total internal volume of the pores of dimensions less than or equal to 40 nm represents at least 60% of the total volume of the material. 3. Porous mineral material according to claim 1 or according to claim 2, characterized in that it has a BET specific surface area at least equal to 1000 m2 per cm3. 4. Porous inorganic material according to any one of claims 1 to 3, characterized in that it has a structure consisting of a joining of hollow objects with external dimensions of between 4 and 28 nanometers, and having a wall thickness of between between 1 and 8 nm, these hollow objects, joined together, themselves defining a porous structure which has pores of dimensions between 10 and 250 nm. 5. Porous inorganic material according to any one of claims 1 to 4, characterized in that it comprises at least one metal oxide, hydroxide or oxy-hydroxide. 6. Porous inorganic material according to any one of claims 1 to 5, characterized in that it comprises at least one silica, an aluminum oxy-hydroxide, an aluminum hydroxide, a zirconium oxide, a hydroxide of rare earth, or a rare earth oxide. 7. Porous mineral material according to any one of <Desc / Clms Page number 23> claims 1 to 6, characterized in that it consists essentially of silica. 8. Porous inorganic material according to claim 7, characterized in that the total pore volume of said material is at least equal to 2 cm3 per gram of material. 9. Porous inorganic material according to claim 7 or according to claim 8, characterized in that it has a BET specific surface area at least equal to 400 m2 per gram. 10. Porous mineral material according to claim 9, characterized in that it has a BET specific surface area of at least 700 m2 per gram. 11. Process for preparing a high porosity mineral material comprising the successive steps consisting in: (a) producing a homogeneous aqueous or hydro-alcoholic medium comprising: (i) an inorganic precursor of a P mineral phase; (ii) dendritic organic polymers comprising surface functionalities (F) capable of forming strong bonds with the mineral precursor (i) or with the mineral phase P; and (iii) nonionic surfactants, said medium being such that, if we denote by n (,) the total amount of mineral precursor (i),), by n (j,) the total amount of polymers (ii) , by n (F) the total quantity of surface functionalities (F) carried by the polymers (ii) and capable of forming strong bonds with the mineral precursor (i) or with the mineral phase P, and by n ,,) the total amount of nonionic surfactants (iii): the molar ratio n (lulu (F) is between 2 and 50; - the molar ratio n (l / n (, l) is between 100 and 5000; and <Desc / Clms Page number 24> the molar ratio n (liiyn (j) is between 0.05 and 0.30; (b) within the medium thus obtained, form a solid mineral phase from the mineral precursor, the total amount of solvent (s) introduced (s) during steps (a) and (b) being such that the concentration of said polymers (ii) in the medium obtained at the end of step (b) is between 0.01 and 10 millimole per liter; and (c) removing dendritic organic polymers and nonionic surfactants within the resulting structure. 12. The method of claim 11, characterized in that the mineral precursor (i) used is a metal compound based on a metal M chosen from silicon, aluminum, zirconium, or rare earths. 13. The method of claim 12, characterized in that the concentration of metal M in the medium of step (a) is between 0.1 and 100 millimoles per liter. 14. The method of claim 11 or of claim 12, characterized in that the mineral precursor (i) of step (a) comprises a silicon alkoxide or a metal silicate whereby the formed mineral phase comprises silica. Si02. 15. Method according to any one of claims 11 to 14, characterized in that the dendritic polymers (ii) each comprise at least 10 functionalities (F) capable of forming strong bonds with the inorganic precursor (i) or with the matrix. mineral P. 16. Method according to any one of claims 11 to 15, characterized in that the mineral precursor (i) used is a compound exhibiting a charge under the conditions of implementation of the method, and in that the surface functionalities ( F) dendritic polymers (ii) are chosen from functions of opposite charge. 17. Method according to any one of claims 11 to 15, characterized in that the inorganic precursor (i) is a silicon alkoxide, and in <Desc / Clms Page number 25> that the surface functionalities (F) of the dendritic polymers (ii) are functions — Si (OR) 3, where R denotes a C1-C8 alkyl group. 18. Method according to any one of claims 11 to 17, characterized in that, in the middle of steps (a) and (b), the average dimensions of the branched structure developed by the dendritic organic polymers (ii) are included. between 1 and 20 nm. 19. Method according to any one of claims 11 to 18, characterized in that the nonionic surfactant (iii) is chosen from poly (ethylene oxide) -poly (propylene oxide) poly (oxide) triblock copolymers. ethylene), or from block copolymers comprising a poly (ethylene oxide) block comprising from 2 to 10 ethoxyl groups, associated with an alkyl or alkanol chain comprising from 8 to 18 carbon atoms. 20. Method according to any one of claims 11 to 19, characterized in that the quantity of polymers (ii) used is such that the concentration of polymers (ii) in the medium obtained at the end of step ( b) is between 0.05 and 1 millimole per liter. 21. Method according to any one of claims 11 to 20, characterized in that the ratio n (i / n (F) is between 5 and 15. 22. Method according to any one of claims 11 to 21, characterized in that the ratio n / nested between 0.07 and 0.2. 23. Method according to any one of claims 11 to 22, characterized in that step (b) is carried out at a temperature between 10 and 100 C. 24. A method according to any one of claims 11 to 23, characterized in that, in step (c), the removal of the polymers (ii) and of the surfactant (iii) is carried out by a heat treatment at a temperature. between 250 and 600 C. 25. Use of a material according to any one of the <Desc / Clms Page number 26> claims 1 to 10 or of a material obtainable according to the process of any one of claims 11 to 24, as absorbent material, as reinforcing material for polymer matrix, as insulating material, or as filler title in a concrete composition.